Add perf tests for readdir and friends

So far tests are not asserting any strict performance requirements, but
instead are going to be used as an easy way to locally measure
performance gains/regressions of changes.

Bug: 158809855
Test: atest com.android.providers.media.client.PerformanceTest
Change-Id: I7c8a9bc3b48568f8a5cdad2ec1eaf35e58d08c98
1 file changed